Electrosurgical instruments which reduces collateral damage to adjacent tissue

ABSTRACT

An electrode assembly for use in combination with an electrosurgical instrument having opposing end effectors and a handle for effecting movement of the end effectors relative to one another. The electrode assembly includes a housing having one portion which is removably engageable with the electrosurgical instrument and a pair of electrodes each having an electrically conductive sealing surface and an insulating substrate. The electrodes are removably engageable with the end effectors of the electrosurgical instrument such that the electrodes reside in opposing relation relative to one another. The dimensions of the insulating substrate are different from the dimensions of the electrically conductive sealing surface to reduce thermal spread to adjacent tissue structures.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.09/387,883 filed on Sep. 1, 1999 which is a continuation of U.S.application Ser. No. 08/968,496 and now issued as U.S. Pat. No.6,050,996 filed on Nov. 12, 1997 the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to electrosurgical instruments used foropen and endoscopic surgical procedures. More particularly, the presentdisclosure relates to a bipolar forceps for sealing vessels and vasculartissue having an electrode assembly which is designed to limit and/orreduce thermal spread to adjacent tissue structures.

TECHNICAL FIELD

A hemostat or forceps is a simple plier-like tool which uses mechanicalaction between its jaws to constrict tissue and is commonly used in opensurgical procedures to grasp, dissect and/or clamp tissue.Electrosurgical forceps utilize both mechanical clamping action andelectrical energy to effect hemostasis by heating the tissue and bloodvessels to coagulate, cauterize and/or seal tissue.

By utilizing an electrosurgical forceps, a surgeon can either cauterize,coagulate/desiccate tissue and/or simply reduce or slow bleeding bycontrolling the intensity, frequency and duration of the electrosurgicalenergy applied to the tissue. Generally, the electrical configuration ofelectrosurgical forceps can be categorized in two classifications: 1)monopolar electrosurgical forceps; and 2) bipolar electrosurgicalforceps.

Monopolar forceps utilize one active electrode associated with theclamping end effector and a remote patient return electrode or pad whichis attached externally to the patient. When the electrosurgical energyis applied, the energy travels from the active electrode, to thesurgical site, through the patient and to the return electrode.

Bipolar electrosurgical forceps utilize two generally opposingelectrodes which are generally disposed on the inner facing or opposingsurfaces of the end effectors which are, in turn, electrically coupledto an electrosurgical generator. Each electrode is charged to adifferent electric potential. Since tissue is a conductor of electricalenergy, when the end effectors are utilized to clamp or grasp tissuetherebetween, the electrical energy can be selectively transferredthrough the tissue.

Over the last several decades, more and more surgeons are complimentingtraditional open methods of gaining access to vital organs and bodycavities with endoscopes and endoscopic instruments which access organsthrough small puncture-like incisions. Endoscopic instruments areinserted into the patient through a cannula, or port, that has been madewith a trocar. Typical sizes for cannulas range from three millimetersto twelve millimeters. Smaller cannulas are usually preferred, which, ascan be appreciated, ultimately presents a design challenge to instrumentmanufacturers who must find ways to make surgical instruments that fitthrough the cannulas.

Certain surgical procedures require sealing blood vessels or vasculartissue. However, due to space limitations surgeons can have difficultysuturing vessels or performing other traditional methods of controllingbleeding, e.g., clamping and/or tying-off transected blood vessels.Blood vessels, in the range below two millimeters in diameter, can oftenbe closed using standard electrosurgical techniques. If a larger vesselis severed, it may be necessary for the surgeon to convert theendoscopic procedure into an open-surgical procedure and thereby abandonthe benefits of laparoscopy.

It is known that the process of coagulating small vessels isfundamentally different than vessel sealing. For the purposes herein theterm “coagulation” is defined as a process of desiccating tissue whereinthe tissue cells are ruptured and dried. The term “vessel sealing” isdefined as the process of liquefying the collagen in the tissue so thatthe tissue cross-links and reforms into a fused mass. Thus, coagulationof small vessels is sufficient to close them, however, larger vesselsneed to be sealed to assure permanent closure.

Several journal articles have disclosed methods for sealing small bloodvessels using electrosurgery. An article entitled Studies on Coagulationand the Development of an Automatic Computerized Bipolar Coagulator, J.Neurosurg., Volume 75, July 1991, describes a bipolar coagulator whichis used to seal small blood vessels. The article states that it is notpossible to safely coagulate arteries with a diameter larger than 2 to2.5 mm. A second article is entitled Automatically Controlled BipolarElectrocoagulation—“COA-COMP”, Neurosurg. Rev. (1984), pp. 187-190,describes a method for terminating electrosurgical power to the vesselso that charring of the vessel walls can be avoided.

In order to effect a proper seal with larger vessels, two predominantmechanical parameters must be accurately controlled—the pressure appliedto the vessel and the gap between the electrodes both of which affectthickness of the sealed vessel. More particularly, accurate applicationof the pressure is important for several reasons: 1) to oppose the wallsof the vessel; 2) to reduce the tissue impedance to a low enough valuethat allows enough electrosurgical energy through the tissue; 3) toovercome the forces of expansion during tissue heating; and 4) tocontribute to the end tissue thickness which is an indication of a goodseal. In some instances a fused vessel wall is optimum between 0.001 and0.006 inches. Below this range, the seal may shred or tear and abovethis range the lumens may not be properly or effectively sealed.

Numerous bipolar electrosurgical instruments have been proposed in thepast for various open and endoscopic surgical procedures. However, someof these designs may not provide uniformly reproducible pressure to theblood vessel and may result in an ineffective or non-uniform seal. Forexample, U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. Nos. 4,005,714 and4,031,898 to Hiltebrandt, U.S. Pat. Nos. 5,827,274, 5,290,287 and5,312,433 to Boebel et al., U.S. Pat. Nos. 4,370,980, 4,552,143,5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern etal., U.S. Pat. No. 5,484,436 to Eggers et al. and U.S. Pat. No.5,951,549 to Richardson et al., all relate to electrosurgicalinstruments for coagulating, sealing and cutting vessels or tissue.

Many of these instruments include blade members or shearing memberswhich simply cut tissue in a mechanical and/or electromechanical mannerand are relatively ineffective for vessel sealing purposes. Otherinstruments generally rely on clamping pressure alone to procure propersealing thickness and are often not designed to take into account gaptolerances and/or parallelism and flatness requirements which areparameters which, if properly controlled, can assure a consistent andeffective tissue seal. For example, it is known that it is difficult toadequately control thickness of the resulting sealed tissue bycontrolling clamping pressure alone for either of two reasons: 1) if toomuch force is applied, there is a possibility that the two poles willtouch and energy will not be transferred through the tissue resulting inan ineffective seal; or 2) if too low a force is applied, a thicker lessreliable seal is created.

It has been found that using electrosurgical instruments to seal tissuemay result in some degree of so-called “thermal spread” across adjacenttissue structure. For the purposes herein the term “thermal spread”refers generally to the heat transfer (heat conduction, heat convectionor electrical current dissipation) traveling along the periphery of theelectrically conductive surfaces. This can also be termed “collateraldamage” to adjacent tissue. As can be appreciated, reducing the thermalspread during an electrical procedure reduces the likelihood ofunintentional or undesirable collateral damage to surrounding tissuestructures which are adjacent to an intended treatment site.

Instruments which include dielectric coatings disposed along the outersurfaces are known and are used to prevent tissue “blanching” at pointsnormal to the sealing site. In other words, these coatings are primarilydesigned to reduce accidental burning of tissue as a result ofincidental contact with the outer surfaces end effectors. So far as isknown these coating are not designed or intended to reduce collateraltissue damage or thermal spread to adjacent tissue (tissue lying alongthe tissue plane).

Several electrosurgical instruments have been introduced which are knownto solve many of the aforementioned problems associated with sealing,cutting, cauterizing and/or coagulating differently-sized vessels. Someof these instruments are described in co-pending U.S. patent applicationSer. No. 09/178,027 filed on Oct. 23, 1998, entitled OPEN VESSEL SEALINGFORCEPS WITH DISPOSABLE ELECTRODES, co-pending U.S. patent applicationSer. No. 09/425,696 filed on Oct. 22, 1999, entitled OPEN VESSEL SEALINGFORCEPS WITH DISPOSABLE ELECTRODES, co-pending U.S. patent applicationSer. No. 09/177,950 filed on Oct. 23, 1998, entitled ENDOSCOPIC BIPOLARELECTROSURGICAL FORCEPS; and co-pending U.S. patent application Ser. No.09/621,029 filed on Jul. 21, 2000, entitled ENDOSCOPIC BIPOLARELECTROSURGICAL FORCEPS, the entire contents of all of which are herebyincorporated by reference herein.

Thus, a need exists to develop an electrosurgical instrument whichincludes an electrode assembly which can seal vessels and tissueconsistently and effectively and reduce the undesirable effects ofthermal spread across tissue structures.

SUMMARY

The present disclosure generally relates to an open and/or endoscopicelectrosurgical instrument which includes a removable electrode assemblyhaving electrodes which are electrically and thermally isolated from theremainder of the instrument by a uniquely designed insulating substrateand electrically conductive surface. It is envisioned that the geometricshape of the insulating substrate relative to the geometric shape of thesealing surface contributes to the overall reduction of collateraldamage to adjacent tissue structures.

More particularly, the present disclosure relates to an electrodeassembly for use with an electrosurgical instrument which includesopposing end effectors and a handle for effecting movement of the endeffectors relative to one another. The assembly includes a housinghaving at least one portion which is removably engageable with at leastone portion of the electrosurgical instrument (e.g., handle, endeffector, pivot, shaft, etc.) and a pair of electrodes. Each electrodepreferably includes an electrically conductive sealing surface and aninsulating substrate and is dimensioned to be selectively engageablewith the end effectors such that the electrodes reside in opposingrelation relative to one another.

Preferably, the dimensions of the insulating substrate are differentfrom the dimensions of the electrically conductive sealing surface toreduce thermal spread to adjacent tissue structures. For example, in oneembodiment of the present disclosure, the cross section of theelectrically conductive sealing surface is different from the crosssection of the insulating substrate which effectively reduces thethermal spread to adjacent tissue.

In other embodiments, the insulating substrate is mounted to theelectrically conductive sealing surface by stamping, by overmolding, byovermolding a stamped seal plate and/or by overmolding a metal injectionmolded seal plate. All of these manufacturing techniques produce anelectrode having an electrically conductive surface which issubstantially surrounded by an insulating substrate. These uniquelydescribed embodiments described herein are contemplated to effectivelyreduce the thermal spread to adjacent tissue structures during and/orimmediately following activation. The electrically conductive sealingsurface may also include a pinch trim which facilitates secureengagement of the electrically conductive surface to the insulatingsubstrate and also simplifies the overall manufacturing process.

In another embodiment, the electrically conductive sealing surfaceincludes an outer peripheral edge which has a radius and the insulatormeets the electrically conductive sealing surface along an adjoiningedge which is generally tangential to the radius and/or meets along theradius. Preferably, at the interface, the electrically conductivesurface is raised relative to the insulator.

The insulating substrate may be made from a plastic or plastic-basedmaterial having a Comparative Tracking Index of about 300 volts to about600 volts. Preferably, the insulating substrate is substrate is madefrom a group of materials which include Nylons,Syndiotactic-polystryrene (SPS), Polybutylene Terephthalate (PBT),Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS),Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate (PET),Polyamide-imide (PAI), Acrylic (PMMA), Polystyrene (PS and HIPS),Polyether Sulfone (PES), Aliphatic Polyketone, Acetal (POM) Copolymer,Polyurethane (PU and TPU), Nylon with Polyphenylene-oxide dispersion andAcrylonitrile Styrene Acrylate. Alternatively, a non-plastic insulatingmaterial, e.g., ceramic, may be used in lieu of or in combination withone or more of the above-identified materials to facilitate themanufacturing process and possibly contribute to uniform and consistentsealing and/or the overall reduction of thermal spread to adjacenttissue structures.

In another embodiment of the present disclosure, the insulatingsubstrate of each electrode includes at least one mechanical interfacefor engaging a complimentary mechanical interface disposed on thecorresponding end effector of the instrument. Preferably, the mechanicalinterface of the substrate includes a detent and the mechanicalinterface of the corresponding end effector includes a complimentarysocket for receiving the detent.

Other embodiments of the present disclosure include a housing having abifurcated distal end which forms two resilient and flexible prongswhich each carry an electrode designed to engage a corresponding endeffector. In another embodiment, the end effectors are disposed at anangle (α) relative to the distal end of the shaft of the electrosurgicalinstrument. Preferably, the angle is about sixty degrees to aboutseventy degrees. The end effectors and, in turn, the electrodes, canalso be dimensioned to include a taper along a width “W” (See FIG. 2).

The present disclosure also relates to an electrode assembly for usewith an electrosurgical instrument having a handle and at least oneshaft for effecting movement of a pair of opposing end effectorsrelative to one another. The electrode assembly includes a housing whichis removably engageable with the shaft and/or the handle and a pair ofelectrodes. Each electrode is removably engageable with a correspondingend effector and includes an electrically conductive sealing surfacewith a first geometric shape and an insulating substrate with a secondgeometric shape. Preferably, the second geometric shape of theinsulating substrate is different from the first geometric shape of thesealing surface which effectively reduces thermal spread to adjacenttissue structures during activation of the instrument.

Preferably, the electrode assembly is removable, disposable andreplaceable after the electrode assembly is used beyond its intendednumber of activation cycles. Alternatively, the electrode assemblyand/or the electrodes may be integrally associated with the endeffectors of the instrument and are not removable. In this instance, theelectrosurgical instrument (open or endoscopic) may be designed forsingle use applications and the entire instrument is fully disposableafter the surgery is completed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an open bipolar forceps according to oneembodiment of the present disclosure;

FIG. 2 is an enlarged, perspective view of a distal end of the bipolarforceps shown in FIG. 1;

FIG. 3 is a perspective view with parts separated of the forceps shownin FIG. 1;

FIG. 4 is an enlarged, side view of an electrode assembly of FIG. 1shown without a cover plate;

FIG. 5 is an enlarged, perspective view of a distal end of the electrodeassembly of FIG. 4;

FIG. 6 is a perspective view with parts separated of an upper electrodeof the electrode assembly of FIG. 5;

FIG. 7A is a perspective view with parts separated of a lower electrodeof the electrode assembly of FIG. 5;

FIG. 7B is a cross section of a prior art electrode configuration withthe electrode extending over the sides of the insulator;

FIG. 7C is a cross section of an electrode with the insulator extendingbeyond the sides of a radiused electrode;

FIG. 7D is a cross section of an overmolded stamped electrodeconfiguration showing the insulator capturing a pinch trim which dependsfrom the electrically conductive surface;

FIG. 7E is a cross section of an electrode configuration showing acompliant barrier disposed about the periphery of the opposingelectrodes and insulators which controls/regulates the heat dissipatingfrom the sealing surface.

FIG. 8A is a perspective view of the open forceps of the presentdisclosure showing the operative motion of the forceps to effect sealingof a tubular vessel;

FIG. 8B is a perspective view of an endoscopic version of the presentdisclosure showing the operative motion of the instrument to effectsealing of a tubular vessel;

FIG. 9 is an enlarged, partial perspective view of a sealing site of atubular vessel;

FIG. 10 is a longitudinal cross-section of the sealing site taken alongline 10-10 of FIG. 9;

FIG. 11 is a longitudinal cross-section of the sealing site of FIG. 9after separation of the tubular vessel;

FIG. 12 is a contour plot showing the dissipation of the electrosurgicalcurrent across the tissue using an electrode without insulation;

FIG. 13A is a contour plot showing the dissipation of theelectrosurgical current across the tissue using an electrode with flushinsulator;

FIG. 13B is an enlarged contour plot of FIG. 13A showing the currentconcentration and relative dissipation of the electrosurgical current atan adjoining edge or interface between the insulator and theelectrically conductive sealing surface;

FIG. 13C is an enlarged electrical field magnitude plot of the electrodeconfiguration of FIG. 13A showing the current concentration and relativedissipation of the electrosurgical field distribution at an adjoiningedge or interface between the insulator and the electrically conductivesealing surface;

FIG. 14A is a contour plot showing the dissipation of theelectrosurgical current across the tissue using an electrode with araised electrically conductive surface and a radiused interface betweenthe electrically conductive surface and the insulator;

FIG. 14B is an enlarged contour plot of FIG. 14A showing the currentconcentration and relative dissipation of the electrosurgical current atan adjoining edge or interface between the insulator and theelectrically conductive sealing surface;

FIG. 14C is an enlarged electrical field magnitude plot of the electrodeconfiguration of FIG. 14A showing the current concentration and relativedissipation of the electrosurgical field distribution at an adjoiningedge or interface between the insulator and the electrically conductivesealing surface; and

FIG. 15 is a contour plot showing the dissipation of the electrosurgicalcurrent across the tissue using an electrode with a raised electricallyconductive surface and a ninety degree (90°) interface between theelectrically conductive surface and the insulator.

DETAILED DESCRIPTION

It has been found that by altering the configuration of the electrodeinsulating material relative to the electrically conductive sealingsurface, surgeons can more readily and easily produce a consistent, highquality seal and effectively reduce thermal spread across or to adjacenttissue. For the purposes herein the term “thermal spread” refersgenerally to the heat transfer (heat conduction, heat convection orelectrical current dissipation) dissipating along the periphery of theelectrically conductive or electrically active surfaces to adjacenttissue. This can also be termed “collateral damage” to adjacent tissue.It is envisioned that the configuration of the insulating material whichsurrounds the perimeter of the electrically conductive surface willeffectively reduce current and thermal dissipation to adjacent tissueareas and generally restrict current travel to areas between theopposing electrodes. As mentioned above, this is different fromdielectrically coating the outer surfaces of the instrument to preventtissue “blanching” at points normal to the sealing site. These coatingsare not designed or intended to reduce collateral tissue damage orthermal spread to adjacent tissue (tissue lying along the tissue sealingplane).

More particularly, it is contemplated that altering the geometricaldimensions of the insulator relative to the electrically conductivesurface alters the electrical path thereby influencing the thermalspread/collateral damage to adjacent tissue structures. Preferably, thegeometry of the insulating substrate also isolates the two electricallyopposing poles (i.e., electrodes) from one another thereby reducing thepossibility that tissue or tissue fluids can create an unintended bridgeor path for current travel. In other words, the insulator andelectrically conductive sealing surface are preferably dimensioned suchthat the current is concentrated at the intended sealing site betweenthe opposing electrically conductive surfaces as explained in moredetail below.

Referring now to FIGS. 1-3, a bipolar forceps 10 for use with opensurgical procedures is shown by way of example and includes a mechanicalforceps 20 and a disposable electrode assembly 21. In the drawings andin the description which follows, the term “proximal”, as istraditional, will refer to the end of the forceps 10 which is closer tothe user, while the term “distal” will refer to the end which is furtherfrom the user. In addition, although the majority of the figures, i.e.,FIGS. 1-7A and 8A, show one embodiment of the presently describedinstrument for use with open surgical procedures, e.g., forceps 20, itis envisioned that the same properties as shown and described herein mayalso be employed with or incorporated on an endoscopic instrument 100such as the embodiment shown by way of example in FIG. 8B.

FIGS. 1-3 show mechanical forceps 20 which includes first and secondmembers 9 and 11 which each have an elongated shaft 12 and 14,respectively. Shafts 12 and 14 each include a proximal end 13 and 15 anda distal end 17 and 19, respectively. Each proximal end 13, 15 of eachshaft portion 12, 14 includes a handle member 16 and 18 attached theretowhich allows a user to effect movement of at least one of the shaftportions, e.g., 12 relative to the other, e.g. 14. Extending from thedistal ends 17 and 19 of each shaft portion 12 and 14 are end effectors24 and 22, respectively. The end effectors 22 and 24 are movablerelative to one another in response to movement of handle members 16 and18.

Preferably, shaft portions 12 and 14 are affixed to one another at apoint proximate the end effectors 24 and 22 about a pivot 25 such thatmovement of one of the handles 16, 18 will impart relative movement ofthe end effectors 24 and 22 from an open position wherein the endeffectors 22 and 24 are disposed in spaced relation relative to oneanother to a clamping or closed position wherein the end effectors 22and 24 cooperate to grasp a tubular vessel 150 therebetween (see FIGS.8A and 8B). It is envisioned that pivot 25 has a large surface area toresist twisting and movement of forceps 10 during activation. It is alsoenvisioned that the forceps 10 can be designed such that movement of oneor both of the handles 16 and 18 will only cause one of the endeffectors, e.g., 24, to move with respect to the other end effector,e.g., 22.

As best seen in FIG. 3, end effector 24 includes an upper or first jawmember 44 which has an inner facing surface 45 and a plurality ofmechanical interfaces disposed thereon which are dimensioned toreleasable engage a portion of a disposable electrode assembly 21 whichwill be described in greater detail below. Preferably, the mechanicalinterfaces include sockets 41 which are disposed at least partiallythrough inner facing surface 45 of jaw member 44 and which aredimensioned to receive a complimentary detent 122 attached to upperelectrode 120 of the disposable electrode assembly 21. While the term“socket” is used herein, it is contemplated that either a male or femalemechanical interface may be used on jaw member 44 with a matingmechanical interface disposed on the disposable electrode assembly 21.

In some cases, it may be preferable to manufacture mechanical interfaces41 along another side of jaw member 44 to engage a complimentarymechanical interface of the disposable electrode assembly 21 in adifferent manner, e.g., from the side. Jaw member 44 also includes anaperture 67 disposed at least partially through inner face 45 of endeffector 24 which is dimensioned to receive a complimentary guide pin124 disposed on electrode 120 of the disposable electrode assembly 21.

End effector 22 includes a second or lower jaw member 42 which has aninner facing surface 47 which opposes inner facing surface 45.Preferably, jaw members 42 and 44 are dimensioned generallysymmetrically, however, in some cases it may be preferable tomanufacture the two jaw members 42 and 44 asymmetrically depending upona particular purpose. In much the same fashion as described above withrespect to jaw member 44, jaw member 42 also includes a plurality ofmechanical interfaces or sockets 43 disposed thereon which aredimensioned to releasable engage a complimentary portion 112 disposed onelectrode 110 of the disposable electrode assembly 21 as describedbelow. Likewise, jaw member 42 also includes an aperture 65 disposed atleast partially through inner face 47 which is dimensioned to receive acomplimentary guide pin 127 (see FIG. 4) disposed on electrode 110 ofthe disposable electrode assembly 21.

Preferably, the end effectors 22, 24 (and, in turn, the jaw members 42and 44 and the corresponding electrodes 110 and 120) are disposed at anangle alpha (α) relative to the distal ends 19, 17 (See FIG. 2). It iscontemplated that the angle alpha (α) is in the range of about 50degrees to about 70 degrees relative to the distal ends 19, 17. It isenvisioned that angling the end effectors 22, 24 at an angle alpha (α)relative to the distal ends 19, 17 may be advantageous for tworeasons: 1) the angle of the end effectors, jaw members and electrodeswill apply more constant pressure for a constant tissue thickness atparallel; and 2) the thicker proximal portion of the electrode, e.g.,110, (as a result of the taper along width “W”) will resist bending dueto the reaction force of the tissue 150. The tapered “W” shape (FIG. 2)of the electrode 110 is determined by calculating the mechanicaladvantage variation from the distal to proximal end of the electrode 110and adjusting the width of the electrode 110 accordingly. It iscontemplated that dimensioning the end effectors 22, 24 at an angle ofabout 50 degrees to about 70 degrees is preferred for accessing andsealing specific anatomical structures relevant to prostatectomies andcystectomies, e.g., the dorsal vein complex and the lateral pedicles.

Preferably, shaft members 12 and 14 of the mechanical forceps 20 aredesigned to transmit a particular desired force to the opposing innerfacing surfaces of the of the jaw members 22 and 24, respectively, whenclamped. In particular, since the shaft members 12 and 14 effectivelyact together in a spring-like manner (i.e., bending that behaves like aspring), the length, width, height and deflection of the shaft members12 and 14 will directly effect the overall transmitted force imposed onopposing jaw members 42 and 44. Preferably, jaw members 22 and 24 aremore rigid than the shaft members 12 and 14 and the strain energy storedin the shaft members 12 and 14 provides a constant closure force betweenthe jaw members 42 and 44.

Each shaft member 12 and 14 also includes a ratchet portion 32 and 34,respectively. Preferably, each ratchet, e.g., 32, extends from theproximal end 13 of its respective shaft member 12 towards the otherratchet 34 in a generally vertically aligned manner such that the innerfacing surfaces of each ratchet 32 and 34 abut one another when the endeffectors 22 and 24 are moved from the open position to the closedposition. Each ratchet 32 and 34 includes a plurality of flanges 31 and33, respectively, which project from the inner facing surface of eachratchet 32 and 34 such that the ratchets 32 and 34 can interlock in atleast one position. In the embodiment shown in FIG. 1, the ratchets 32and 34 interlock at several different positions. Preferably, eachratchet position holds a specific, i.e., constant, strain energy in theshaft members 12 and 14 which, in turn, transmits a specific force tothe end effectors 22 and 24 and, thus, the electrodes 120 and 110.

In some cases it may be preferable to include other mechanisms tocontrol and/or limit the movement of the jaw members 42 and 44 relativeto one another. For example, a ratchet and pawl system could be utilizedto segment the movement of the two handles into discrete units whichwill, in turn, impart discrete movement to the jaw members 42 and 44relative to one another.

Preferably, at least one of the shaft members, e.g., 14, includes a tang99 which facilitates manipulation of the forceps 20 during surgicalconditions as well as facilitates attachment of electrode assembly 21 onmechanical forceps 20 as will be described in greater detail below.

As best seen in FIGS. 2, 3 and 5, disposable electrode assembly 21 isdesigned to work in combination with mechanical forceps 20. Preferably,electrode assembly 21 includes housing 71 which has a proximal end 77, adistal end 76 and an elongated shaft plate 78 disposed therebetween. Ahandle plate 72 is disposed near the proximal end 77 of housing 71 andis sufficiently dimensioned to releasably engage and/or encompass handle18 of mechanical forceps 20. Likewise, shaft plate 78 is dimensioned toencompass and/or releasably engage shaft 14 and pivot plate 74 disposednear the distal end 76 of housing 71 and is dimensioned to encompasspivot 25 and at least a portion of distal end 19 of mechanical forceps20. It is contemplated that the electrode assembly 21 can bemanufactured to engage either the first or second members 9 and 11 ofthe mechanical forceps 20 and its respective component parts 12, 16 or14, 18, respectively.

In the embodiment shown in FIG. 3, handle 18, shaft 14, pivot 25 and aportion of distal end 19 are all dimensioned to fit into correspondingchannels located in housing 71. For example, a channel 139 isdimensioned to receive handle 18, a channel 137 is dimensioned toreceive shaft 14 and a channel 133 is dimensioned to receive pivot 25and a portion of distal end 19.

Electrode assembly 21 also includes a cover plate 80 which is alsodesigned to encompass and/or engage mechanical forceps 20 in a similarmanner as described with respect to the housing 71. More particularly,cover plate 80 includes a proximal end 85, a distal end 86 and anelongated shaft plate 88 disposed therebetween. A handle plate 82 isdisposed near the proximal end 85 and is preferably dimensioned toreleasable engage and/or encompass handle 18 of mechanical forceps 20.Likewise, shaft plate 88 is dimensioned to encompass and/or releasableengage shaft 14 and a pivot plate 94 disposed near distal end 86 isdesigned to encompass pivot 25 and distal end 19 of mechanical forceps20. Preferably, handle 18, shaft 14, pivot 25 and distal end 19 are alldimensioned to fit into corresponding channels (not shown) located incover plate 80 in a similar manner as described above with respect tothe housing 71.

As best seen with respect to FIGS. 3 and 4, housing 71 and cover plate80 are designed to engage one another over first member, e.g., 11, ofmechanical forceps 20 such that first member 11 and its respectivecomponent parts, e.g., handle 18, shaft 14, distal end 19 and pivot 25,are disposed therebetween. Preferably, housing 71 and cover plate 80include a plurality of mechanical interfaces disposed at variouspositions along the interior of housing 71 and cover plate 80 to effectmechanical engagement with one another. More particularly, a pluralityof sockets 73 are disposed proximate handle plate 72, shaft plate 78 andpivot plate 74 of housing 71 and are dimensioned to releasably engage acorresponding plurality of detents (not shown) extending from coverplate 80. It is envisioned that either male or female mechanicalinterfaces or a combination of mechanical interfaces may be disposedwithin housing 71 with mating mechanical interfaces disposed on orwithin cover plate 80.

As best seen with respect to FIGS. 5-7A, the distal end 76 of electrodeassembly 21 is bifurcated such that two prong-like members 103 and 105extend outwardly therefrom to support electrodes 110 and 120,respectively. More particularly, electrode 120 is affixed at an end 90of prong 105 and electrode 110 is affixed at an end 91 of prong 103. Itis envisioned that the electrodes 110 and 120 can be affixed to the ends91 and 90 in any known manner, e.g., friction-fit, slide-fit, snap-fitengagement, crimping, etc. Moreover, it is contemplated that theelectrodes 110 and 120 may be selectively removable from ends 90 and 91depending upon a particular purpose and/or to facilitate assembly of theelectrode assembly 21.

A pair of wires 60 and 62 are connected to the electrodes 120 and 110,respectively, as best seen in FIGS. 4 and 5. Preferably, wires 60 and 62are bundled together and form a wire bundle 28 (FIG. 4) which runs froma terminal connector 30 (see FIG. 3), to the proximal end 77 of housing71, along the interior of housing 71, to distal end 76. Wire bundle 28is separated into wires 60 and 62 proximate distal end 76 and the wires60 and 62 are connected to each electrode 120 and 110, respectively. Insome cases it may be preferable to capture the wires 60 and 62 or thewire bundle 28 at various pinch points along the inner cavity of theelectrode assembly 21 and enclose the wires 60 and 62 within electrodeassembly 21 by attaching the cover plate 80.

This arrangement of wires 60 and 62 is designed to be convenient to theuser so that there is little interference with the manipulation ofbipolar forceps 10. As mentioned above, the proximal end of the wirebundle 28 is connected to a terminal connector 30, however, in somecases it may be preferable to extend wires 60 and 62 to anelectrosurgical generator (not shown).

As best seen in FIG. 6, electrode 120 includes an electricallyconductive seal surface 126 and an electrically insulative substrate 121which are attached to one another by snap-fit engagement or some othermethod of assembly, e.g., overmolding of a stamping or metal injectionmolding. Preferably, substrate 121 is made from molded plastic materialand is shaped to mechanically engage a corresponding socket 41 locatedin jaw member 44 of end effector 24 (see FIG. 2). The substrate 121 notonly insulates the electric current but it also aligns electrode 120both of which contribute to the seal quality, consistency and thereduction of thermal spread across the tissue. Moreover, by attachingthe conductive surface 126 to the substrate 121 utilizing one of theabove assembly techniques, the alignment and thickness, i.e., height“h2”, of the electrode 120 can be controlled. For example and as bestillustrated in the comparison of FIGS. 7B and 7C, the overmoldingmanufacturing technique reduces the overall height “h2” (FIG. 7C) of theelectrode 120 compared to traditional manufacturing techniques whichyield a height of “h1” (FIG. 7B). The smaller height “h2” allows a useraccess to smaller areas within the body and facilitates sealing aroundmore delicate tissue areas.

Moreover, it is contemplated that the overmolding technique providesmore insulation along the side of the electrically conductive surfacewhich also reduces thermal spread due to less electrode to tissuecontact. It is envisioned that by dimensioning substrate, e.g., 121 andelectrode 120 in this fashion (i.e., with reduced conductive surfacearea), the current is restricted (i.e., concentrated) to the intendedseal area rather than current traveling to tissue outside the seal areawhich may come into contact with an outer edge of the electrode 120 (seeFIG. 7B).

Preferably, substrate 121 includes a plurality of bifurcated detents 122which are shaped to compress during insertion into sockets 41 and expandand releasably engage sockets 41 after insertion. It is envisioned thatsnap-fit engagement of the electrode 120 and the jaw member 44 willaccommodate a broader range of manufacturing tolerances. Substrate 121also includes an alignment or guide pin 124 which is dimensioned toengage aperture 67 of jaw member 44. A slide-fit technique is alsocontemplated such as the slide-fit technique describe with respect tocommonly-assigned, co-pending U.S. application Ser. No. 203-2348CIP2PCT,by Tetzlaff et al., the entire contents of which is hereby incorporatedby reference herein.

Conductive seal surface 126 includes a wire crimp 145 designed to engagethe distal end 90 of prong 105 of electrode assembly 21 and electricallyengage a corresponding wire connector affixed to wire 60 located withinelectrode assembly 21. Seal surface 126 also includes an opposing face125 which is designed to conduct an electrosurgical current to a tubularvessel or tissue 150 when it is held thereagainst.

Electrode 110 includes similar elements and materials for insulating andconducting electrosurgical current to tissue 150. More particularly,electrode 110 includes an electrically conductive seal surface 116 andan electrically insulative substrate 111 which are attached to oneanother by one of the above methods of assembly. Substrate 111 includesa plurality of detents 112 which are dimensioned to engage acorresponding plurality of sockets 43 and aperture 65 located in jawmember 42. Conductive seal surface 116 includes an extension 155 havinga wire crimp 119 which engages the distal end 91 of prong 103 andelectrically engages a corresponding wire connector affixed to wire 62located in housing 71. Seal surface 116 also, includes an opposing face115 which conducts an electrosurgical current to a tubular vessel ortissue 150 when it is held thereagainst. It is contemplated thatelectrodes 110 and 120 can be formed as one piece and include similarcomponents and/or dimensions for insulating and conducting electricalenergy in a manner to effectively reduce thermal spread.

As mentioned above, it is envisioned that thermal spread may be reducedby altering the physical dimensions of the insulators and theelectrodes, e.g., by altering the geometry/shape of the insulator. It isenvisioned that manufacturing the electrodes 110 and 120 in this fashionwill reduce thermal spread and stray currents that may travel to theelectrosurgical instrument. Stray current may be further restricted bycasting the forceps and/or manufacturing the forceps using anon-conductive material and/or coating the edges of the electrodes 110and 120 with an insulative coating.

For example and as best shown in the comparison of FIG. 7B (prior art)with newly disclosed FIGS. 7C, 7D, 14A and 14B substrates 111, 121 aredesigned to extend along width “W” (FIG. 2) such that the width of theinsulating substrate, e.g., 111, exceeds the width of the electricallyconductive seal surface, e.g., 116. It is envisioned that theseelectrically conductive sealing surface 116 and insulator 111configurations may be accomplished by various manufacturing techniquessuch as overmolding of a stamping and/or metal injection molding.Stamping is defined herein to encompass virtually any press operationknown in the trade, including, but not limited to: blanking, shearing,hot or cold forming, drawing, bending and coining. Other manufacturingtechniques may also be employed to achieve similar electricallyconductive sealing surface 116 and insulator 111 configurations whichwill effectively reduce thermal spread to adjacent tissue.

It is envisioned that manufacturing the electrodes 110 and 120 in thisfashion will reduce thermal spread to adjacent tissue structures and,possibly, reduce the electric field potential which will, in turn,reduce stray currents traveling through the instrument body. The varyinggeometry of the insulator 111 compared to the electrically conductivesurface 116 also isolates the two opposing poles during activationthereby reducing the possibility that tissue or tissue fluids willbridge a path for stray current travel to surrounding tissue. As bestseen in FIG. 7D, the electrode 116 may also include a pinch trim 131which facilitates secure, integral engagement of the insulate 111 andthe electrically conductive sealing surface 116 during the assemblyand/or manufacturing process.

FIG. 7E shows another embodiment of the present disclosure wherein acompliant material 161 is disposed about the outer peripheries of theelectrically conductive sealing surfaces 116, 126 and the substrates111, 121. it is envisioned that the compliant material 161 acts as amechanical barrier by restricting heat and steam emanating from thesealing surface thereby reduces thermal spread to surrounding tissue.One or more barriers 161 may be attached to the end effectors 22, 24and/or the insulting substrate 111, 121 depending upon a particularpurpose of to achieve a particular result.

FIGS. 14A, 14B, 14C and 15 show the electrically conducive sealingsurfaces 116, 126 raised relative to the insulative coatings orinsulators 111, 121. Preferably, the electrically sealing surface 116,126 is radiused or curved which reduces current concentration and thedissipation of stray currents to surrounding tissue structures. It iscontemplated that the insulators 111, 121 and electrically conductivesealing surfaces 116, 126 can be dimensioned to meet at or generallyalong interfaces or adjoining longitudinally-oriented edges 129, 139which are radiused to reduce current concentrations 141 and currentdissipation proximate the interfaces 129, 139 and opposing electricallyconductive surfaces 116, 126.

For example and by way of illustration, FIGS. 12 and 13A-13C show otherelectrode 110, 120 configurations which are known in the prior art. FIG.12 shows an example of uninsulated (i.e., without insulators 111, 121)opposing electrodes 110, 120 during activation illustrating theelectrical field distribution 135 emanating from the opposingelectrically conductive sealing surfaces 116, 126 (it is known thatcurrent flows perpendicular to these electrical field lines). As can beappreciated, the electrical field 135 emanates well beyond the intendedtreatment site which can contribute to increased collateral tissuedamage and possibly cutting.

By providing insulators 111, 121 which are flush with the electricallyconductive sealing surfaces 116, 126 as shown in FIGS. 13A-13C, theelectrical field distribution 135 can be significantly reduced. However,as the enlarged views of FIGS. 13B and 13C illustrate, a currentconcentration 141 tends to develops between opposing electricallyconductive surfaces 116, 126 and at or proximate interfaces 129, 139.This current concentration 141 may also lead to negative effects andpossibly cause cutting of the tissue or sticking of the tissue to theelectrode or electrically conductive surfaces at this site.

FIGS. 14A-15 show various electrode 110, 120 configurations according tothe present disclosure in which the electrically conductive sealingsurfaces 116, 126 and the insulators 111, 121 are designed to reduce theamount of current concentration 141 between opposing electrodes 110,120. More particularly, FIGS. 14A and 14B show a pair of raisedelectrically conductive sealing surfaces 116, 126 (relative to theinsulators 111, 121) which include outer peripheries 145, 147 havingradii “r” and “r′”, respectively. Preferably, insulators 111, 121 meetouter peripheries 145, 147 and form adjoining edges or interfaces 129,139 which track along radii “r” and “r′”, respectively. It iscontemplated that configuring the electrodes 110, 120 in this mannerwill effectively reduce the current concentration 141 between the outerperipheries 145, 147 of the opposing electrically conductive sealingsurfaces 116, 126.

As can be appreciated, configuring the electrically conductive sealingsurfaces 116, 126 and insulators 111, 121 with this unique profile,additionally provides a more uniform, consistent and more easilycontrollable electrical field distribution 135 across the adjacenttissue structures. Turning back to FIG. 7C, it is envisioned thatinsulator 111 may also meet outer periphery 145 in a generallytangential fashion about radius “r”. Again, this profile also tends toreduce current concentration and thermal spread.

FIG. 15 also shows the insulators 111, 121 and the electricallyconductive sealing surfaces 116, 126 meeting at an angle of ninetydegrees (90°), however, the insulator 111, 121 is positioned furtherfrom the radiused edge 145 of the electrically conductive sealingsurface 116, 126. It is envisioned that too much exposure of the edge145 may initiate the formation of new and/or additional stray currentsor electrical fields proximate the interface 129, 139 thereby nullifyingthe benefits of manufacturing the surface 116, 126 with a radiused edge145.

Preferably, the radius “r” and “r′” of the outer peripheries 145, 147 ofthe electrically conductive sealing surfaces are about the same and areabout ten thousandths of an inch to about thirty thousandths of an inch.However, it is contemplated that each radii “r” and “r′” may be sizeddifferently depending upon a particular purpose or to achieve a desiredresult.

In some cases it may be preferable to utilize different materials whichmay facilitate the manufacturing process and possibly supplement overallthermal spread reduction. For example, a variety of materials arecontemplated which include nylons and syndiotactic polystryrenes such asQUESTRA® manufactured by DOW Chemical. Other materials may also beutilized either alone or in combination, e.g., PolybutyleneTerephthalate (PBT), Polycarbonate (PC), Acrylonitrile Butadiene Styrene(ABS), Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate(PET), Polyamide-imide (PAI), Acrylic (PMMA), Polystyrene (PS and HIPS),Polyether Sulfone (PES), Aliphatic Polyketone, Acetal (POM) Copolymer,Polyurethane (PU and TPU), Nylon with Polyphenylene-oxide dispersion andAcrylonitrile Styrene Acrylate.

Utilizing one or more of these materials may produce other desirableeffects, e.g., reduce the incidence of flashover. These effects arediscussed in detail in concurrently-filed, co-pending, commonly assignedapplication Ser. No. [203-2657] entitled “ELECTROSURGICAL INSTRUMENTWHICH IS DESIGNED TO REDUCE THE INCIDENCE OF FLASHOVER” by Johnson etal.

Alternatively, certain coatings can be utilized either alone or incombination with one of the above manufacturing techniques to supplementoverall thermal spread reduction.

FIG. 8A shows the bipolar forceps 10 during use wherein the handlemembers 16 and 18 are moved closer to one another to apply clampingforce to the tubular tissue 150 to effect a seal 152 as shown in FIGS. 9and 10. Once sealed, the tubular vessel 150 can be cut along seal 152 toseparate the tissue 150 and form a gap 154 therebetween as shown in FIG.11.

After the bipolar forceps 10 is used or if the electrode assembly 21 isdamaged, the electrode assembly 21 can be easily removed and/or replacedand a new electrode assembly 21 may be attached to the forceps in asimilar manner as described above. It is envisioned that by making theelectrode assembly 21 disposable, the electrode assembly 21 is lesslikely to become damaged since it is only intended for a singleoperation and, therefore, does not require cleaning or sterilization. Asa result, the functionality and consistency of the sealing components,e.g., the electrically conductive surface 126, 116 and insulatingsurface 121, 111 will assure a uniform and quality seal and provide atolerable and reliable reduction of thermal spread across tissue.Alternatively, the entire electrosurgical instrument may be disposablewhich, again, will assure a uniform and quality seal with minimalthermal spread.

FIG. 8B shows an endoscopic bipolar instrument 100 during use whereinmovement of a handle assembly 128 applies clamping force on the tubulartissue 150 to effect a seal 152 as shown in FIGS. 9-11. As shown, ashaft 109 and the electrode assembly 122 are inserted through a trocar130 and cannula 132 and a handle assembly 118 is actuated to causeopposing jaw members of the electrode assembly 122 to grasp tubularvessel 150 therebetween. More particularly, a movable handle 118 b ismoved progressively towards a fixed handle 118 a which, in turn, causesrelative movement of the jaw members from an open, spaced-apart positionto a closed, sealing position. A rotating member 123 allows the user torotate the electrode assembly 122 into position about the tubular tissue150 prior to activation.

After the jaw members are closed about the tissue 150, the user thenapplies electrosurgical energy via connection 128 to the tissue 150. Bycontrolling the intensity, frequency and duration of the electrosurgicalenergy applied to the tissue 150, the user can either cauterize,coagulate/desiccate seal and/or simply reduce or slow bleeding withminimal collateral or thermal damage to surrounding tissue.

From the foregoing and with reference to the various figure drawings,those skilled in the art will appreciate that certain modifications canalso be made to the present disclosure without departing from the scopeof the present disclosure. For example, although it is preferable thatelectrodes 110 and 120 meet in parallel opposition, and, therefore, meeton the same plane, in some cases it may be preferable to slightly biasthe electrodes 110 and 120 to meet each other at a distal end such thatadditional closure force on the handles 16 and 18 is required to deflectthe electrodes in the same plane. It is envisioned that this couldimprove seal quality and/or consistency.

Although it is preferable that the electrode assembly 21 include housing71 and cover plate 80 to engage mechanical forceps 20 therebetween, insome cases it may be preferable to manufacture the electrode assembly 21such that only one piece, e.g., housing 71 is required to engagemechanical forceps 20.

It is envisioned that the outer surface of the end effectors may includea nickel-based material, coating, stamping, metal injection moldingwhich is designed to reduce adhesion between the end effectors (orcomponents thereof) with the surrounding tissue during or after sealing.

While only one embodiment of the disclosure has been described, it isnot intended that the disclosure be limited thereto, as it is intendedthat the disclosure be as broad in scope as the art will allow and thatthe specification be read likewise. Therefore, the above descriptionshould not be construed as limiting, but merely as exemplifications of apreferred embodiment. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

1. An electrode assembly for use with an electrosurgical instrumenthaving opposing end effectors and a handle for effecting movement of theend effectors relative to one another, comprising: a housing having atleast one portion which removably engages at least one portion of theelectrosurgical instrument; and a pair of electrodes each including anelectrically conductive sealing surface and an insulating substrate, theelectrodes being removably engageable with respective end effectors ofthe electrosurgical instrument such that the electrodes reside inopposing relation relative to one another, the dimensions of theinsulating substrate differing from the dimensions of the electricallyconductive sealing surface to reduce thermal spread to adjacent tissuestructures, wherein the insulating substrate is made from a materialhaving a Comparative Tracking Index of about 300 volts to about 600volts.
 2. An electrode assembly according to claim 1 wherein theinsulating substrate is selected from the group consisting of nylon,syndiotactic-polystryrene, polybutylene terephthalate, polycarbonate,acrylonitrile butadiene styrene, polyphthalamide, polymide, polyethyleneterephthalate, polyamide-imide, acrylic, polystyrene, polyether sulfone,aliphatic polyketone, acetal copolymer, polyurethane, nylon withpolyphenylene-oxide dispersion and acrylonitrile styrene acrylate.
 3. Anelectrode assembly according to claim 1 wherein the insulating substrateis mounted to the electrically conductive sealing surface by overmoldinga stamped seal plate.
 4. An electrode assembly according to claim 1wherein the insulating substrate is mounted to the electricallyconductive sealing surface by overmolding a metal injection molded sealplate.
 5. An electrode assembly according to claim 1 wherein theelectrically conductive sealing surface of at least one electrodeincludes a pinch trim and the insulating substrate extends beyond aperiphery of the electrically conductive sealing surface.
 6. Anelectrode assembly according to claim 1 wherein the insulating substrateof each of the electrodes includes at least one mechanical interface forengaging a complimentary mechanical interface disposed on thecorresponding end effector of the instrument.
 7. An electrode assemblyaccording to claim 6 wherein the mechanical interface of at least one ofthe substrates includes at least one detent and the mechanical interfaceof the corresponding end effector includes at least one complimentarysocket for receiving the detent.
 8. An electrode assembly according toclaim 1 wherein the housing includes a bifurcated distal end which formstwo prongs and each prong is removably attached to one of the endeffectors.
 9. An electrode assembly according to claim 1 wherein atleast one of the opposing end effectors and the corresponding at leastone electrode is tapered.
 10. An electrode assembly according to claim 1wherein the end effectors are disposed at an angle relative to the shaftof the electrosurgical instrument.
 11. An electrode assembly accordingto claim 10 wherein the angle is about sixty degrees to about seventydegrees.
 12. An electrode assembly according to claim 1 wherein theelectrode assembly is disposable.
 13. An electrode assembly for use withan electrosurgical instrument having a handle and at least one shaft foreffecting movement of a pair of opposing end effectors relative to oneanother, comprising: a housing having at least one portion whichremovably engages at least one of the handle and the shaft; a pair ofelectrodes each having an electrically conductive sealing surface havinga first geometric shape and an insulating substrate having a secondgeometric shape, the electrodes being removably engageable withrespective end effectors of the instrument such that the electrodesreside in opposing relation relative to one another, the secondgeometric shape of the insulating substrate differing from the firstgeometric shape of the sealing surface to reduce thermal spread toadjacent tissue structures; and wherein the insulating substrate is madefrom a material having a Comparative Tracking index of about 300 voltsto about 600 volts.
 14. An electrode assembly according to claim 13wherein the electrically conductive sealing surface of at least oneelectrode includes a pinch trim and the insulating substrate extendsbeyond the periphery of the electrode.
 15. An electrode assemblyaccording to claim 13 wherein the insulating substrate is selected fromthe group consisting of nylon, syndiotactic-polystryrene, polybutyleneterephthalate, polycarbonate, acrylonitrile butadiene styrene,polyphthalamide, polymide, polyethylene terephthalate, polyamide-imide,acrylic, polystyrene, polyether sulfone, aliphatic polyketone, acetalcopolymer, polyurethane, nylon with polyphenylene-oxide dispersion andacrylonitrile styrene acrylate.
 16. An electrode assembly according toclaim 13 wherein the insulating substrate is mounted to the electricallyconductive sealing surface by overmolding a stamped seal plate.
 17. Anelectrode assembly according to claim 13 wherein the insulatingsubstrate is mounted to the electrically conductive sealing surface byovermolding a metal injection molded seal plate.
 18. An electrodeassembly for use with a disposable electrosurgical instrument having ahandle and at least one shaft for effecting movement of a pair ofopposing end effectors relative to one another, comprising: a housing; apair of electrodes each having an electrically conductive sealingsurface having a first geometric shape and an insulating substratehaving a second geometric shape, the electrodes being integrallyassociated with respective end effectors of the instrument such that theelectrodes reside in opposing relation relative to one another; whereinthe second geometric shape of the insulating substrate differs from thefirst geometric shape of the sealing surface to reduce thermal spread toadjacent tissue structures, and wherein the insulating substrate has aComparative Tracking index of about 300 volts to about 600 volts.